闽北东坑火山盆地白垩纪火山—侵入杂岩的岩石成因与金成矿  

Petrogenesis and gold mineralization of Cretaceous volcanic-intrusive complex in Dongkeng volcanic basin,northern Fujian

作　　者：徐丽娟 徐夕生[1] XU Lijuan;XU Xisheng(State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing,210023)

机构地区：[1]南京大学地球科学与工程学院,内生金属矿床成矿机制研究国家重点实验室,南京210023

出　　处：《地质论评》2024年第6期2381-2399,共19页Geological Review

基　　金：国家自然科学基金资助重点项目(编号:41930214)的成果。

摘　　要：火山岩和侵入岩是许多浅成低温热液型金矿床成矿物质和流体的重要来源。中生代时期华南陆块经历了强烈的岩浆—热液活动,在中国东南沿海地区形成了大量的火山—侵入杂岩和浅成低温热液金矿。笔者等选取该区研究程度较低的闽北政和县东坑火山盆地为研究对象,利用岩相学、年代学、全岩地球化学、Sr—Nd—Hf同位素等方法,来探讨该火山盆地中火山岩和侵入岩的成因联系、岩浆演化过程以及它们与盆地内同时期金矿的关系。东坑火山盆地由多种岩性的火山岩和空间上与其密切共生的浅成侵入相花岗斑岩、石英二长斑岩,以及携带暗色微粒包体的花岗岩脉组成。LA-ICP-MS锆石U-Pb定年显示,东坑的火山岩和侵入岩均形成于白垩纪(101.0±0.9~97.3±1.2 Ma),其全岩Sr—Nd同位素组成较均一[n(^(87)Sr)/n(^(86)Sr)]_(i){=0.7085~0.7104;ε_(Nd)(t)=-8.83~-7.34},但锆石Hf同位素组成变化范围较大[ε_(Hf)(t)=-14.0~3.3]。岩石地球化学特征显示,该盆地火山—侵入杂岩为富碱、富钾的准铝—弱过铝质岩石,这些岩石具有连续线性变化的主量元素特征、右倾的稀土配分曲线、弱至中等的Eu负异常(Eu/Eu∗=0.19~0.83)、较高的氧逸度(lgfO_(2)=-17.44~-4.18)以及大离子亲石元素Rb、K、Pb富集,高场强元素Nb、Ta、Ti亏损的特征。综合年代学及岩石地球化学特征,认为东坑火山盆地中的火山—侵入杂岩是在古太平洋板块俯冲后撤的伸展构造背景下,幔源岩浆上涌促使地壳源岩发生重新熔融并与之混合,不断演化,最终侵位于地壳浅表的产物。岩浆的源区组成、结晶分异和高氧逸度条件等共同造就了该盆地及周围同时期金的成矿。Objectives:Volcanic and intrusive rocks serve as important sources of ore-forming materials and fluids in many epithermal gold deposits.The South China Block has experienced strong magmatic—hydrothermal activities during the Mesozoic time,producing a large number of volcanic—intrusive complexes and epithermal gold deposits along the coastal area of southeast China.This study select the Dongkeng volcanic basin in Zhenghe County,northern Fujian Province,which was less studied,to explore the genetic relationship between its volcanic and intrusive rocks,their magmatic evolution process,and their relationship with gold mineralization.Methods:Based on the field work,we conducted petrological,geochronology,whole-rock geochemistry,and Sr—Nd—Hf isotopes studies of the Dongkeng volcanic—intrusive complex.Results:The Dongkeng volcanic basin is composed of various lithological volcanic rocks and coexisting shallow intrusive rocks,including porphyritic granite,porphyritic quartz monzonite,and mafic microgranular enclaves bearing granite dykes.The LA-ICP-MS zircon U-Pb dating results show that the volcanic and intrusive rocks in Dongkeng were formed in the Cretaceous(101.0±0.9~97.3±1.2 Ma).All the rocks have consistent Sr,Nd isotopic compositions with[n(^(87)Sr)/n(^(86)Sr)]_(i)values of 0.7085~0.7104 andε_(Nd)(t)values of-8.83~-7.34.However,their zircon Hf isotopic compositions are highly variable withε_(Hf)(t)values ranging from-14.0 to+3.3.Geochemically,the volcanic—intrusive rocks in Dongkeng volcanic basin show high potassium,high alkaline,metaluminous to weakly peraluminous features,and have linear variation in the Harker diagrams,high oxygen fugacity(lgfO_(2)=-17.44~-4.18).In chondrite-normalized REE distribution patterns and primitive mantlenormalized trace element spidergrams,all lithologies are enriched in LREEs compared with HREEs,and they have weakly to moderately negative europium anomalies(Eu/Eu∗=0.19~0.83)and are enriched in Rb,K,Pb,and depleted in Nb,Ta,Ti.Conclusions:Based on the geochronologi

关 键 词：东坑火山盆地 火山—侵入杂岩 浅成低温热液型金矿 岩石成因 

分 类 号：P618.51[天文地球—矿床学]